Image forming apparatus having loop forming rollers in accordance with respective sheet feed units

Abstract

An image forming apparatus includes a plurality of sheet feed units each for feeding a sheet, a single pair of registration rollers provided at the upstream side of the image formation site where an image is formed on the sheet with respect to the direction of sheet conveyance, for conveying the sheet in accordance with the timing of forming the image on the sheet, and a plurality pair of loop forming rollers provided in correspondence with the plurality of sheet feed units respectively at the upstream side of the pair of registration rollers with respect to the direction of sheet conveyance. Each of the plurality pair of loop forming rollers is controlled in a manner such that a loop is formed between each of the plurality pair of loop forming rollers and the pair of registration rollers.

What is claimed is:  
     
       1. An image forming apparatus comprising: 
       (a) a plurality of sheet feeding units each for feeding a sheet, each of the sheet feeding units comprising a conveying out roller for feeding the sheet from a sheet cassette, a drive roller, and a driven roller in contact with the drive roller for feeding the sheet fed by the conveying out roller;  
       (b) a single registration means for conveying the sheet in synchronization with a timing of forming an image on the sheet;  
       (c) a plurality of loop forming means each provided on an upstream side in a sheet conveyance direction with respect to the single registration means in accordance with each of the plurality of sheet feeding units, the plurality of loop forming means being positioned downstream of each of the sheet feeding units; and  
       (d) a controller for controlling each of the plurality of loop forming means to form a loop of the sheet between the single registration means and each of the plurality of loop forming means.  
     
     
       2. The image forming apparatus of  claim 1  further comprising a reversing mechanism for turning the sheet upside down which has a reversing path for switching the sheet conveyance direction over to an opposite direction, 
       wherein the sheet which has been switched in the opposite direction at the reversing path, is controlled to form a loop between the single registration means and a loop forming means by said loop forming means that is disposed closest to the reversing path among the plurality of loop forming means.  
     
     
       3. The image forming apparatus of  claim 2 , wherein the reversing mechanism is disposed in a main body of the image forming apparatus. 
     
     
       4. The image forming apparatus of  claim 1 , wherein each of the plurality of sheet feeding units has an accommodating section for accommodating sheets and a sheet feeding means for feeding a sheet one by one, 
       wherein the sheet feeding means provided in accordance with each of the plurality of sheet feeding units is provided in a position different from one another with respect to a width direction of the image forming apparatus.  
     
     
       5. The image forming apparatus of  claim 4  further comprising a reversing mechanism for turning the sheet upside down which is disposed vertically in a side portion of a side on which each of the plurality of sheet feeding means is disposed. 
     
     
       6. The image forming apparatus of  claim 1 , wherein each of the plurality of loop forming means is set in a condition of sheet gripping force different from one another in accordance with each of conveyance paths from the loop forming means to the single registration means.